Apparatus for removing random fluctuations from intensity measurements



c. J. GIBBS ETAL APPARATUS FOR RE March 30, 1948. 2,438,747

MOVING RANDOM FLUCTUATIONS FROM INTENSITY MEASUREMENTS Original Filed March 4, 1944 INVENTOR 3 Cd. 6/553.

(@441 J M JTAV/V.

ATTOR Y Patented Mar. 30, I

APPARATUS FOR R FLUCTUATIONS EN TS Clifford J. Gibbs, Laingsburg,

Toms River, N. 1., Development Corporation, New corporation of Delaware Original application March 525,050. Divided and her 22, 1945, Serial No H. Stein,

EMOVIN G RANDOM FROM INTENSITY Micln, and James assignors to Texaco York, N. Y., a

4, 1944, Serial No.

this application Septem- 1 Claim. (Cl. 73-430) This invention relates to the measuring or recording, or both, of variable intensities the true values of which are marked by random fluctuations, and more particularly to an apparatus for smoothing out random or satistical fluctuations which occur, for example, in the logging of formations traversed by a bore hole or well, wherein variations in the radioactivity of the formations are measured as an indication of the nature or character of the formations. Another application of the invention is in the removing of fluctuations which occur in making an electrical log (resistance log and self-potential log) of a well, and which fluctuations are due to irregularities in the contact of the electrodes with the surrounding medium and to other accidental causes. Still another application of the same idea relates to the smoothing out of irregularities in the plate current of radio tubes. such irregularities are due to the random nature of electron emission by the cathode of the tube.

This application is a, division of our application Serial No. 525,050 filed March 4, 1944 in which is also disclosed an electrical circuit by means of which a smooth record may be obtained.

The principal object of the present invention is to provide a device for smoothing out a record so as to prevent confusion which might be caused by random fluctuations without, however, destroying the usefulness of the record by also eliminating peaks or dips in the record which are pertinent and meaningful as indications, for instance. of the presence of underground formations having different radioactivity from the adjacent formations.

It is obvious, of course, that the random fluctuations in the value of a measurement may be reduced to any desired fraction of their original amplitude by means of a suitable low-pass filter, mechanical or electrical. Also, it is true that while such a filter will transmit long-time variations in the average level, it reduces the amplitude of short-time variations to a great extent.

It is in the transmission of these short-time variations in the average level of the measurement that the simple low-pass filter is unsatisfactory, and it was a search for a filter which would respond to short-time indications which led to the present invention.

In accordance with the present embodiment of the invention a mechanical device smooths out the random or statistical fluctuations. In this form of the invention the mirror or a pen of the recording galvanometer is mounted on a block or frame which is supported on the arm or needle .tively to the frame It of the galvanometer by springs. The springs sorb small movements of the arm caused by random fluctuations but permit the block to follow movements indicating changes of the average intensity.

For a better understanding of the invention reference may behad to the accompanying drawing which is a perspective view of a mechanical device embodying the principles of the invention.

Referring to the drawing, the single flgure shows a mechanical device for preventing random fluctuations from appearing in an intensity record. The arm l0 represents the indicating pointer of an instrument such as a recording galvanometer and is pivoted as is shown at 12. A frame member or hollow block II has aflixed thereto a pen or mirror indicated diagrammatically at It so that movements of the frame in a direction of its longitudinal axis may be recorded either on a moving sheet of paper, not shown, or by means of a beam of light reflected from the mirror to a photosensitive surface such as a moving film. The frame It is supported from the two opposite sides of the arm I It by means of resilient springs l8 so that slight movements or vibrations of the arm in will be absorbed by the resiliency of the springs without causing movement of the frame it, which, because of its inertia, has resistance to movement. However, when the average intensity of the quantity to be measured increases or decreases, one of the springs will be completely compressed so that movement of the arm I 0 will be transmitted posiand thus to the marking or indicating device I8 so that these movements of the arm due to actual variations in the quantity to be measured will be recorded. With the marking device resiliently attached to the arm it, as by means 01' the springs i8, random fluctuations will be eliminated or materially smoothed out so that an intelligible record will result. The amplitude of the fluctuations which are to be suppressed can be controlled by changing the width of the slot 20 in the frame or block it or by movmeans such as a dashpot, but this is not essential.

The essential feature in this invention is the fact that its suppression of short-time fluctualarge enough to accommodate the amplitude of the fluctuations which are to be suppressed; any fluctuation of greater amplitude than this, regardless of how short is its duration, will be recorded, whereas, with a simple shock-absorber arrangement in which the arm I!) were never allowed to strike the frame II, the same shorttime fluctuation would be appreciably suppressed. If the desired fluctuation were of a sufliciently short duration, it is possible that it would be completely lost in the smoothing action of the simple shock-absorber, or low-pass filter, while with the device embodying'this invention the fact that the excursion is of short duration is of no consequence provided only that its amplitude exceeds thepredetermined critical amplitude at which the arm strikes the frame and imparts to the latter a positive motion.

Although the invention is described in connection with the measuring or recording of natural radioactivity, it is to be understood that it is also applicable in measuring other forms of radioactivity such as scattered neutrons and gamma rays, as well as in the measuring or recording of other quantities-in fact, whenever a continuous indication of intensity measurements generally is desired.

Obviously many modifications and variations of the invention, as hereinbetore set forth, may be made without departing from the spirit and scope thereof, but only such limitations should be imposed as are indicated in the appended claim.

We claim: An instrument for indicating continuous variations in a quantity, said instrument having a pointer arm movable in response to said variations and also in response to random fluctuations, means for smoothing out said random fluctuations comprising an inertia member provided with a slot in the plane of movement or the pointer arm, an indicating device on said inertia member, the outer end portion of said pointer arm projecting into said slot, and compression springs between opposite sides of said end portion of the. pointer arm and the walls of the inertia member at the ends of the slot, said springs serving to absorb movements of said pointer arm caused by said random fluctuations and to transmit to said inertia member and indicating device movements of the pointer arm caused by average variations in said quantity.

CLIFFORD J. GIBBS. JAMES H. STEIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Kiene July 2'7, 1943 

